During an experiment, they found that typically average-looking faces are considered more trustworthy than attractive ones.

“Face typicality likely indicates familiarity and cultural affiliation. These findings have important implications for understanding social perception, including cross-cultural perceptions and interactions," explained lead researcher Carmel Sofer from Princeton University in New Jersey and Radboud University Nijmegen in the Netherlands.

Sofer and colleagues wondered whether typicality might be more directly tied to perceptions of trustworthiness. In one experiment, they created a "typical" face by digitally averaging 92 female faces and also created an "attractive" face by averaging the 12 most attractive faces from another set of faces. They then combined both faces into one and created nine variations that had differing levels of attractiveness and typicality. The final result was a continuum of 11 faces which ranged from least attractive to most attractive, with the most typical face occupying the midpoint.

Female participants viewed these face variations and used a nine-point scale to rate them on either trustworthiness or attractiveness; over the course of the study, the participants saw and rated each face three times. The researchers only included female participants so as to eliminate potential cross-gender differences in how people perceive and evaluate faces.

The resulting ratings revealed a sort of U-shaped relationship between face typicality and trustworthiness: The closer a face was to the most typical face, the more trustworthy it was considered to be."By showing the influence of face typicality on perceived trustworthiness, our findings cast a new light on how face typicality influences social perception," the researchers wrote.

The study was published in Psychological Science, a journal of the Association for Psychological Science.